Substations in high and medium-voltage power networks include primary devices such as electrical cables, lines, bus bars, switches, power transformers and instrument transformers, which are generally arranged in switch yards and/or bays. These primary devices are operated in an automated way via a Substation Automation (SA) system. The SA system comprises secondary devices, so-called Intelligent Electronic Devices (IED), responsible for protection, control and monitoring of the primary devices. The IEDs may be assigned to hierarchical levels, i.e. the station level, the bay level, and the process level, the latter being separated from the bay level by a so-called process interface. The station level of the SA system includes an Operator Work Station (OWS) with a Human-Machine Interface (HMI) and a gateway to a Network Control Centre (NCC). IEDs on the bay level, also termed bay units, in turn are connected to each other as well as to the IEDs on the station level via an inter-bay or station bus primarily serving the purpose of exchanging commands and status information. IEDs on the process-level comprise electronic sensors for voltage (VT), current (CT) and gas density measurements, contact probes for sensing switch and transformer tap changer positions, and/or intelligent actuators (I/O) for controlling switchgear like circuit breakers or disconnectors. Exemplary process-level IEDs such as non-conventional current or voltage transformers comprise an Analogue to Digital (AD) converter for sampling of analogue signals. Process-level IEDs are connected to the bay units via a process bus, which can be considered as the process interface replacing a conventional hard-wired process interface.
A communication standard for communication between the secondary devices of a substation has been introduced by the International Electrotechnical Committee (IEC) as part of the standard IEC 61850 entitled “communication networks and systems in substations”. For non-time critical messages, IEC 61850-8-1 specifies the Manufacturing Message Specification (MMS, ISO/IEC 9506) protocol based on a reduced Open Systems Interconnection (OSI) protocol stack with the Transmission Control Protocol (TCP) and Internet Protocol (IP) in the transport and network layer, respectively, and Ethernet as physical media. For time-critical event-based messages, IEC 61850-8-1 specifies the Generic Object Oriented Substation Events (GOOSE) directly on the Ethernet link layer of the communication stack. For very fast periodically changing signals at the process level such as measured analogue voltages or currents IEC 61850-9-2 specifies the Sampled Value (SV) service, which like GOOSE builds directly on the Ethernet link layer. Hence, the standard defines a format to publish, as multicast messages on an industrial Ethernet, event-based messages and digitized measurement data from current or voltage sensors on the process level. SV and GOOSE messages are transmitted over a process bus.
SA systems based on IEC 61850 are configured and described by means of a standardized configuration representation or formal system description called System Configuration Description (SCD). An SCD file comprises the logical data flow between the IEDs on the basis of message types or data sets, i.e. for every message source, a list of destination or receiver IEDs, the message size in terms of data set definitions, as well as the message sending rates for all periodic traffic like GOOSE, SV and Integrity reports. The SCD file likewise comprises the relation between the IEDs as well as the functionality which the IEDs execute on behalf of the substation process or switch yard.
IEC 61850 not only specifies the method of the data transfer but also defines the process data of the servers. For that purpose, IEC 61850 uses an object-oriented approach with Logical Nodes (LN) as core objects which can be grouped under different Logical Devices (LD). A LN is a functional grouping of data with corresponding attributes and represents the smallest entity that may be independently implemented in, or hosted by, an individual IED. Examples are all data of a circuit breaker contained in the Logical Node XCBR or all data of a timed overcurrent protection contained in the Logical Node PTOC. There are LNs for data/functions related to LDs (LLNO) and for common device properties of physical devices (LPHD).
SA systems include a number of basic SA functions for protecting, controlling, or monitoring of the substation, which functions relate to individual pieces of primary equipment or to entire substation parts such as bays, voltage levels or bus bars. In the exemplary context of protection typical such functions are distance protection, line protection, breaker failure protection and differential protection. In addition, higher-level applications are provided, which may concern more than one piece of primary equipment, and which include station-level interlocking, station and bay level switching sequences, transformer parallel control, transformer auto close functions, as well as any other kind of load transfer and/or shedding.
The standard IEC 61850 defines basic features which can be used to set up functional and performance tests inside a distributed system, in particular for SA systems with serial or process-bus connection to the process. As even a segment-wise isolation of the process-bus for the purpose of testing a specific protection function and thereby disabling all other functions sharing the process bus segment is not acceptable for operating or live systems, specific operating modes have been introduced. For instance, only a Logical Node in a “test” mode as coded by the value of the “Beh” data object of the LN and indicated in the “q” attribute of all its other data objects accepts test signals with an input signal quality attribute “test”. These test signals include preconfigured or predefined test data stored on the host device. In case of missing test signals, the LN in “test” mode also accepts live data obtained from the actual operating process. On the other hand, an IED in “simulation” mode as coded by the “Sim” attribute inside the IED's LPHD allows the IED to switch to simulated data exclusively received via simulated GOOSE or SV data sets as coded by a corresponding flag in the respective GOOSE or SV message header.
These modes thus determine how input signal test quality works together with the LN modes. Further features within the testing concept include a “test blocked” mode for deactivating hardware output signals thus preventing actions on a primary equipment level, and “mirror back” signals (opRcvd, opOk) of actions at all process related output signals.
However, the above concept ignores the fact that only for the most basic functions the totality of the involved LNs and hosting IEDs is easily identifiable. In fact, any slightly more complex functionality may involve one or several intermediary LNs logically interconnected between an input LN and output LN that are under control of the tester. In a conservative approach, any test on an operating system demands a straightforward and complete deactivation of all parts of the substation, i.e. of the bays, voltage levels or bus bar sections possibly concerned by the test, in order to prevent any uncontrolled, let alone detrimental operation of a piece of primary equipment.
The patent application EP 2203754 is concerned with the operation of substations in which protection, control and measurement IEDs exchange operational data over a data network, for instance according to IEC standard 61850. During maintenance, commissioning and fault situations when one or several IEDs are inoperable, the data that these IEDs would have produced is substituted to ensure availability of the substation. To this effect, a dedicated substitute device is permanently installed that can take the role of any missing IED, and that is automatically configured out of the SCD file that describes the SA system. The simulated operational data may comprise status information or process values assigned to an unrepresented piece of primary substation equipment and substituting real data determined by a sensor connected to the piece of primary equipment.
In the patent application EP 2362577, every network message configured for transmission from a sender to a receiver IED across an Ethernet switch-based communication network of a PC or SA system is evaluated, and a graphical representation respective of process related operational aspects of each IED involved is generated and displayed. From a logical data flow description that is part of a formal configuration representation of the PC or SA system, sender and receiver IEDs are retrieved or determined. Likewise, a single one out of a plurality of operational aspect of the process is retrieved for each IED from the formal configuration description. Generating the graphical representation of the system includes forming groups of IEDs with identical operational aspects. For each group of IEDs, the respective operational aspect is indicated or displayed, in the form of a label or tag, along with, or otherwise linked to, the group. As a consequence, a user may easily analyze the communication configuration of the system by looking at the generated graphical representation and determine, at a single glance, the consequences of IED failures or engineering errors on other IEDs and/or on the controlled and protected process.
WO 2009/135512 relates to a method for examining a communication connection between field devices of an automation system for electrical energy supply networks. A first field device is made to issue, by way of a testing device, a test data telegram to at least one other field device through a communication network belonging to the communication connection to be tested. At least one other field device sends a confirmation telegram to the testing device after receiving the test data telegram, and the testing device displays the receipt of all confirmation telegrams received as a reaction to the test data telegram.
The principles and methods of the following invention are by no means restricted to a use in substation automation, but likewise applicable to other process control systems with a formal system description. In particular, it has to be noted that IEC 61850 is also an accepted standard for Hydro power plants, Wind power systems, and Distributed Energy Resources (DER).